Sanding machine



K- C. ATKIN SANDING mommy 2 Sheets-She t 1 Filed April 14, 19

HH IIIR U -llIll-l l Aug. 2, 19490 c, ATKIN 2,478,074

SANDING MACHINE Filed April 14, 1948 2 Sh99t5 s et 2 "ulls I lg.

Patented Aug. 2, 1949 SANDING MACHINE Kenneth C. Atkin, Muskegon, Mich., asslgnor to Clarke Sanding Machine Company, Muskegon, Mich, a corporation of Michigan Application April 14, 1948, Serial No. 21,002

3 Claims. 1

The present invention relates to sanding machines and particularly to an improved sanding pad construction, characterized by a novel combination and arrangement of parts to provide a firm, yet resilient and yielding backing for a sand paper disc, and at the same time to provide adequate means for dissipating the heat generated by the action of the abrasive on the work.

In any sanding machine of the type wherein a sandpaper disc is rotated against a work surface at high speed considerable heat is developed by the fricition oi the abrasive on the work. Un-- less this heat is dissipated rapidly, it will of necessity result in an undue temperature rise of the pad on which the abrasive sheet is mounted, as well as on the sandpaper itself and on the work surface. This is manifestly undesirable, not only because of the deleterious effects of high temperature on the work surface and on the abrasive sheet, but particularly because it is necessary that the paper be mounted on a thick resilient pad which, while firm enough to provide substantial support for the paper, is nevertheless yieldable. An ideal material for the pad is rubber, and with such a pad it is obvious that an unnecessarily high operating temperature is undesirable, since it tends to shorten the life of a rubber, and cause it to harden and lose its desired resilience.

The problem of providing adequate cooling for a pad of the character contemplated is a difiicult one, and withstanding the fact that numerous efiorts have been made to solve it, the problem nevertheless continues to persist. This is no doubt due to the fact that to be satisfactory from a physical standpoint the material of the pad must be quite dense though somewhat yielding, and it is a natural characteristic of materials having these physical characteristics, such as rubber, that they possess a low degree of thermal conductivity and are thus ordinarily unable to adequately dissipate the heat generated at their surfaces.

It is accordingly the primary object of the present invention to provide a sanding pad including a relatively firm and solid, yet resilient and yieldable backing for an abrasive sheet, so designed and constructed that the heat generated by the action of the abrasive is readily dissipated from the pad, in order that the operating temperature of the Dad be maintained at a minimum.

A further object of the invention resides in the provision of the combination of a pad as indicated above, together with a housing structure and a suction system aranged to serve a double function, by acting as a dust collector in the usual manner, and in addition coating with the pad to further increase the eificiency of its heat dissipating means.

The foregoing objects are accomplished according to the present invention by the provision of a sanding pad wherein the surface on which the abrasive sheet is mounted consists of a generally flat disc of firm, yet resilient and yicldable material, such as semihard rubber, but wherein the rubber pad is reenforced and supported by a metal plate and provided with what may be termed double-action means for dissipating heat. By the term double-action, it is meant that the pad is provided with means not only adapted to dissipate heat directly from the rubber material of the pad, but in addition includes means for drawing the heat ofi indirectly, by utilizing the high thermal conductivity of the metal backing plate of the pad to conduct heat from the more remote portions of the pad to air channels at spaced intervals. A flow of cool air is maintained, through the air channels, and the channels are so formed that air passing through them takes heat from the metal backing sheet as well as directly from the rubber. The utility of this type of construction is further increased by an arrangement of a pad guard and suction system, including the usual means to collect dust, but wherein the guard and suction inlet are so related to theair passages of the pad as to further increase the flow of cool air through the passages and facilitate the cooling action of the air.

A present preferred construction for utilizing the principles of the present disclosure is illustrated in the drawings attached to and forming a part of this specification, wherein:

Figure 1 is a fragmental sectional view of a rotary disc sanding machine, the machine including a resilient padand suction system as contemplated by the present invention;

Figure 2 is a fragmental bottom plan view of the machine;

Figure 3 is a top plan view of a sanding disc, constructed in accordance with these teachings;

Figure 4 is a central detail sectional view of the pad, and is taken substantially on the plane of the line 4-4 of Figure 3; and

Figure 5 is a detail sectional view taken substantially on the plane of the line 5-5 of Figure 3.

The sanding pad of the present invention is illustrated in connection with a sanding machine more fully described and claimed in my copending application, Seral No. 21,001, filed April 14, 1948, and while it is deemed unnecessary to go into an extended discussion of all of the features of the machine it may be briefly pointed out that it includes a. motor and fan housing In and gear case II, with a suction fan l2 mounted on the shaft l3 of the motor and a pinion M on the l wer end of the motor shaft arranged to mesh with a speed reduction gear i5 carried on an upright spindle IS. The spindle is rotatably mounted in antifriction bearings ii and i8, and the lower end of the spindle is threaded into the hub fitting 2i of the sanding pad.

The pad itself includes a fairly thick resilient rubber body portion 22, intimately bonded t0 a rigid sheet metal backing plate 23, which is in turn secured to the hub portion 2|, as by a plurality of rivets 24. The sanding pad is arranged to carry an abrasive sheet 25, such as sandpaper or emery cloth, on its lower surface. If desired, the opposite sides of the pad may be slightly tapered with respect to each other, so that when the machine is held in a position with the axis of the spindle l6 inclined a few degrees from vertical, the pad will contact a horizontal work surface on one side only and will thus be effective to sand a relatively narrow strip, so that the width of the operating surface of the disc is somewhat less than the radius of the pad. The abrasive sheet 25 is held in place at the hul'v of the pad by a flanged washer 26, secured in p sition by cap screw 21, threaded into the end of the spindle IS. A circular guard 3i is preferably mounted on a gear cover 32 of the gear case, and this guard includes a downwardly curved flange 33 lying closely adjacent the edge of the pad around its entire circumference.

The machine is also provided with a dust pickup system comprising a suction nozzle 35 extending over half of the circumference of the pad and located just outside of the pad radius, so that dust raised by the action of the abrasive on the work is drawn upwardly through the nozzle passage to the fan i 2 and thence discharged into a dust bag.

According to the present invention, the pad 22 is provided with a plurality of radially extending air channels 36, each extending outwardly from an inlet opening 31 in the flange 38 of the hub fitting 2| to an outlet port 39 at the extreme outer edge of the pad. These channels 36 may vary somewhat in size, number and configuration, but highly satisfactory results have been obtained by a construction utilizing eight radial channels equally spaced about the circumference of the pad with each of the channels molded in substantially square cross sections and positioned immediately below the backing plate 23, so that the bottom and side surfaces of each channel are in direct communication with the rubber material of the pad, while the top surface of each channel is formed by the sheet metal of the backing plate. Thus, when the disc is rotated at high speed, the channels 38 act in the manner of a centrifugal fan, drawing cool air inwardly through the ports 31 and discharging it from the ports 39. This supplies a constant flow of air through each of the channels, and. the cool air passing through the warmer material of the rub- -ber is effective to dissipate the heat sufficiently to maintain the temperature of the pad or degrees below the operating temperature in a pad of similar size and shape formed without these passages.

It is to be noted that the flow of air through the channels 36 not only dissipates heat directly from the surface of the rubber but also serves to pass air along the underside of the metal backing plate23, so that heat generated in portions of the pad between the adjoining channels and somewhat remote from the channel surfaces will be transmitted through the thermally conductive metal plate to the air channels and thence indirectly carried away. This accomplishes doubleaction cooling and increases the efiiciency of the heat dissipating means.

The sanding pad, as thus far described, is adapted for use on any conventional type of disc sanding machine, but it is particularly advantageous in combination with a machine having a structure as shown in Figures 1 and 2, since the new combination of the air passages providing direct and indirect cooling of the pad coact with the particular type of dust suction system shown in the machine to achieve a particularly successful result.

It will be noted that the flanges 33 of the guard 3i surround the outer edges of the pad 22 fairly closely, and that the rear of the guard is closely fitted to the inwardly extending flange 4| of the gear housing, so that any substantial fiow of air between the outer surface of the guard and the housing is prevented. The guard includes a plurality of openings 42, however, and (while these openings serve to permit the operator to insert a screw driver through the openings 43 in the pad and thus loosen the screws 44 of the gear cover, as described in my other application) they also serve as inlets for cool air from above the pad. Thus, a constant supply of airmay fiow inwardly through the openings 42 and thence into the inlet ports 31 and outwardly through the channels 36 to the outlet ports 39. These ports are positioned immediately adjacent the suction passage 35, so that the flow of air through the passages 36 due to centrifugal action is further increased by the suction exerted by the fan l2 of the machine. Thus the suction system, with the dust nozzle adjacent the outlet ports of the pad and air inlets nearer its center acts in combination with the centrifugal action of the disc to dissipate heat from the sanding surface with sufiicient rapidity to maintain the body of the pad at a relatively low operating temperature. It follows that the mechanical advantages inherent in the use of a pad having a thick and firm rubber surface are retained, yet the difiiculties heretofore encountered in attempting to dissipate the heat generated by the abrasive action are overcome. The operating temperature of the pads is thus low, so that the rubber of the pads does not deteriorate rapidly, and the undesirable effects oi. excessive temperature on the work and the abrasive sheets are avoided.

The precise form of the invention shown is intended for purposes of illustration only. not as a limitation on the scope of the present disclosure. It should accordingly be recognized that various modifications and variations of the present teachings may be indulged in without departure from the inventive concept, as defined by the following claims.

Having thus described the invention, what I claim as new and desire to protect by United States Letters Patent is:

1. In combination, a sanding pad including a relatively thick circular disc of firm but resilient and yieldable material, with a hub fitting positioned centrally of the disc whereby it may be rotated; said disc including a plurality of radially extending channels, each of said channels having an inlet port adjacent the hub fitting of the disc and an outlet port adjacent its outer edge,

whereby rotation of the pad will cause an air flow through the channels to dissipate heat from the pad; together with a disc guard substantially surrounding the sanding disc, said guard having a flange closely adjacent-the outer circumference of the disc, and having at least one air inlet port located inwardly of said flange to permit air to pass through the guard to the inlet ports of the disc, and a suction channel extending around and immediately adjacent the flange of the guard throughout a substantial portion of the circumference of the disc, whereby the flow of air through the channels of the pad will be increased by the action of the suction channel at the outlet ports of the pad.

2. In a sanding machine, a sanding pad including a mounting fitting adapted to support the pad on a driving shaft for rotation therewith; a resilient and yieldable pad face adapted to carry a sheet of abrasive material; a thin sheet of material of high thermal conductivity extending substantially across the entire area of the pad face, and a plurality of substantially radial channels through the pad face, the channels having an inlet port near the mounting fitting and outlet ports near the edge of the pad, said channels being directly adjacent the sheet of thermally conductive material whereby air flowing through the channels may dissipate heat from the portions of the pad adjacent the channels directly, while heat from more remote portions of the pad will be conducted to the channels by the sheet of thermally conductive material and dissipated indirectly.

3. In a sanding machine, a sanding pad including a mounting fitting adapted to support the pad on a driving shaft for rotation therewith; a resilient and yieldable pad face adapted to carry a sheet of abrasive material; a reenforcing member comprising a single thin disc of metal of high thermal conductivity extending substantially across the entire area of the pad face and in intimate bonded contact with the material of the pad face. and a plurality of substantially radial channels through the pad face; each'channel including an inlet port near the mounting fitting and an outlet port near the edge of the pad; said channels being directly adjacent the metal disc, whereby air flowing through the channels may dissipate heat from the portions of the pad adjacent the channels directly, while heat from more remote portions of the pad will be conducted to the channels by the metal reinforcing disc and dissipated indirectly.

KENNETH C. ATKIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

